Electric hair trimmers or clippers (interchangeable here) are commonly used by stylists, barbers, or individuals for styling the hair of others. However, it is known to provide an electric hair clipping device designed specifically for self-cutting. One such self-cutting electric hair trimmer (see, e.g., commonly-assigned U.S. Pat. No. 4,118,863, to Sandy, issued Oct. 10, 1978, and incorporated by reference herein) is somewhat effective for non-skilled hair trimming and thinning, e.g., between professional haircuts. An important feature of the '863 patent is the provision of a moving blade with teeth extending past the relatively shorter teeth of the fixed or stationary blade. One benefit of such an arrangement is that the longer moving blade teeth help to move and randomly cut the hair, creating a general thinning rather than cutting a uniform swath through the hair, as would a more conventional clipper. However, such a trimmer presents at least two related problems.
The '863 patent features a bladeset with moving teeth shaped to guide relatively small amounts of hair into a cutting zone formed by an overlap between the moving teeth and shorter stationary teeth. Generally, the depth of this cutting zone is on the order of two to three perpendicular diameters of a human hair. If two hairs are “stacked” in the cutting zone, with one hair in the part nearest to a root of either of the stationary and moving teeth, and one hair adjacent to it but farther from the teeth roots and protruding from the cutting zone, the protruding hair may be nicked, or may be cut only partially through. This nicked or partially cut hair may sever and fall off several days after the trim, an undesirable result, and in some cases misleading the user that hair is being lost.
Further, at least some typical conventional hair trimmers are shaped to be held in a way that is inconvenient for self-cutting. More specifically, the trimmers are shaped so that they are difficult to hold such that the angle of attack (the angle made by the plane of the cutting zone and the hair strands to be cut) of the bladeset is substantially perpendicular to the hairs to be cut, such as the hairs on the back of a self-user's head. When the angle of attack is substantially not perpendicular, the hairs enter the cutting zone at an oblique angle. This not only exacerbates the problem of “stacked” hairs in the cutting zone described above, but presents a situation in which the elongated cross-section of a single hair at an oblique angle to the cutting zone may exceed the cutting zone depth, leading to the same nicking or partial cutting described above.
In instances when the user attempts to cut the back of his head at the appropriate angle of attack, the wrist must be angled sharply or “cocked” to one side. This resulting position, known as ulnar deviation, is a biochemical deviation that may cause pain, discomfort, or even tendonitis, especially when the position is held for extended periods.
Such ergonomic considerations are also an issue when one person cuts another person's hair. At least some conventional hair trimmers are shaped to be held in a way that is inconvenient for cutting other's hair. This is especially the case for users with limited hand and/or arm mobility, such as sufferers from arthritis or injuries to the hand and/or arm.
Accordingly, there is a need for an improved self-cutting hair trimmer which reduces the amount of nicking and/or partial cutting of hair caused by conventional self-cutting hair trimmers. There is also a need to provide for the more effective guiding of hairs into or retaining of hairs in a cutting zone of a bladeset of a hair trimmer. There is still another need for a hair trimmer holdable by a self-user or hair stylist such that the bladeset angle of attack is substantially perpendicular to the hair to be cut on all areas of the head, without causing discomfort to the user when holding the trimmer for self-cutting, or by the stylist when cutting the hair of another.